1. Field of the Invention
This invention relates to flexible optical fibers, particularly those in the form of a twisted flexible optical fiber bundle, for use in a viewing device for observing the image of areas outside the field of view of an observer, comprising at least one object lens fixed to observe areas outside the field of view of an observer, an image forming unit, such as a display, installed in front of the observer, and flexible optical fibers connected at one end to the at least one object lens and at the other end to the image forming unit, thereby to transmit an image received by the object lens through the flexible optical fibers to the image-forming unit where the image is formed. This invention further relates to a viewing device in which such a specific bundle of flexible optical fibers is used.
2. Description of the Prior Art
Vehicles, for example, automobiles have heretofore been provided with devices for viewing outward scenes, such as a room rearview mirror and side view mirrors used in combination, however, these viewing devices have many defects derived from their design and structure. Even if the room rearview mirror and side view mirrors are used in combination, the most serious defect found in this case is to produce dead spaces or dead angles, for example, just behind the automobile. In the case of large-sized cars, such dead spaces are produced even at outer sides of the car. Further, it is necessary for the driver to shift his sight from up to down and from left to right in order to confirm safety at the sides or rear side of the automobile while it is driven. This is an important problem from the view-point of safety.
In addition, as to a room rearview mirror in an automobile, there are raised problems that a small mirror provides a small view of the rearward scene, while too large a mirror hinders the forward field of view. Further, such too large a mirror tend to allow the driver and fellow passengers to hazardously hit their head against the mirror when the automobile causes an accident such as collision or sudden stop and also tend to limit their movement in the room of the automobile. Still further, there is raised a problem that the rearward field of view is hindered due to the rear window being clouded when it is heavily snowing or raining.
On the other hand, as to the side view mirrors fixed on the outer walls of the automobile, there are raised problems that the side view mirrors are very liable to injure the driver and pedestrians since they are not only protruded from the roof and side walls of the automobile, but also liable to scrape roadside trees. Further, it raises problems as to safety that at night such side view mirrors reflecting lights from rearward vehicles have a blinding effect and allow snow to be attached thereto on a snowy day. Furthermore, side view mirrors are, per se, so limited in their position to be installed and shape to be taken that they may easily provide a side view of the outward scene, whereby they are made commonplace in style and are disadvantageous in that they produce comparatively great air resistance when the automobile runs.
In view of the defects of the conventional rearview mirrors, particularly the safety thereof, many attempts have been made to provide improved rearview devices as exemplified below.
The improved rearview devices proposed include a rearview device (Japanese published Utility Model Application No. 51-30752) comprising three plane mirrors combined together in a housing fixed on the automobile body portion just above the windshield of an automobile, a rearview device (Japanese published patent application No. 56-6891) which enables even a smaller mirror to provide a certain wide angle field of view under certain conditions by refracting incident rays of light in the direction of normal line thereby shortening the path of the light by the use of prisms placed in a housing fixed on the same body portion as above, and a rearview device using a television camera.
However, with said rearview device comprising the three mirrors, it will be difficult for any driver to obtain a constant field of view because of the structure of the combined mirrors in cases where they are small in size, and it will take a time for a remarkably tall-bodied or short-bodied driver to adjust the mirrors. On the other hand, in cases where such mirrors are large in size, there will be raised many problems as to their fixing, appearance and the like. Said rearview device comprising the prisms eliminates the aforesaid defects, however, it still produces dead angles (or dead spaces) rearward and downward of the vehicle body, the dead angles becoming a problem particularly when the vehicle is backed. These proposed rearview devices do not eliminate the drawbacks of the conventional rearview mirrors, but only solve a part of the above problems. Further, said rearview device using a television camera is disadvantageous in that the camera portion is difficult to produce in the miniaturized form and the outward protrusions thereof are consequently remarkable. Still further, the weakest points of the device using a television camera are that since the camera and the like comprise many electronic components, they are vulnerable to vibration thereby raising a problem as to their durability and they will stop their operation due to a power failure.